Our invention relates generally to a system for graphical data interpretation, storage, transmission and the like, and more particularly to an electrographic sensor which may be placed over graphical data to be analyzed or have the graphical data optically projected against the rear surface of the sensor. The term "graphical data" as used herein, is any source of information presentable in two dimensions. In addition, the term "lucent" is defined to cover all transparencies from clear to translucent (see Webster's Dictionary). The term "processed," as used in conjunction with data, is intended to cover interpretation, storage, transmission and the like.
Considerable effort has been expended in recent years toward apparatus for graphical data processing. Many of the devices developed for this purpose utilize orthogonal electrical fields in a sensor unit together with a probe that is movable across the sensor to derive a signal proportional to the position of the probe. These signals may be in analog or digital form. The most pertinent prior art known to us are the devices described in U.S. Pat. No. 3,632,874 issued to Lucien C. Malavard on Jan. 4, 1972, and U.S. Pat. No. 3,798,370 issued to George S. Hurst on Mar. 19, 1974.
The patent to Hurst teaches a construction of an electrographic sensor whereby very accurate position-related signals can be obtained. This involves the use of spot electrodes along the edge of an opaque resistive paper in the sensor, and discrete resistors connected between adjacent electrodes to form resistor networks across which voltages are applied to produce uniform orthogonal electric fields. However, the structure can only be used to process data placed on top of the sensor. This prevents its use in such applications as those associated with cathode ray display tubes or optical projection from the rear of any sort.
In the patent to Malavard, one embodiment is described for copying graphical data. He specifically mentions cathode ray display tubes. No teaching is given in the patent, however, as to the composition of the "thin conduction layer" applied to the "substrate." Whatever the composition, the transparency of the sensor is reduced substantially according to his admission. Also, Malavard does not teach how he would produce the terminals along the edge of the unit. Furthermore, he teaches the use of a graphite stylus to contact the sensor. We know from previous experience that this is damaging to surfaces and causes a relatively short sensor lifetime.
Accordingly, no suitable transparent and highly accurate electrographic sensor was known in the art. Furthermore, no sensor was known whereby projected images of data could be processed.